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Cycles: Optimization for Heterogeneous Volume Shadows.

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* Don't compute expf() for every step, instead sum the intermediate values and calculate it every N (8 for now) steps. This helps a few percent (~5% on a cube with wave texture) in my tests here.
This commit is contained in:
Thomas Dinges 2014-08-14 20:09:25 +02:00
parent 8ff3cf3e56
commit 5af00a3d12
1 changed files with 16 additions and 8 deletions
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24
intern/cycles/kernel/kernel_volume.h
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@ -176,6 +176,8 @@ ccl_device void kernel_volume_shadow_heterogeneous(KernelGlobals *kg, PathState
/* compute extinction at the start */
float t = 0.0f;
float3 sum = make_float3(0.0f, 0.0f, 0.0f);
for(int i = 0; i < max_steps; i++) {
/* advance to new position */
float new_t = min(ray->t, (i+1) * step);
@ -190,20 +192,26 @@ ccl_device void kernel_volume_shadow_heterogeneous(KernelGlobals *kg, PathState
/* compute attenuation over segment */
if(volume_shader_extinction_sample(kg, sd, state, new_P, &sigma_t)) {
/* todo: we could avoid computing expf() for each step by summing,
* because exp(a)*exp(b) = exp(a+b), but we still want a quick
* tp_eps check too */
tp *= volume_color_transmittance(sigma_t, new_t - t);
/* Compute expf() only for every Nth step, to save some calculations
* because exp(a)*exp(b) = exp(a+b), also do a quick tp_eps check then. */
/* stop if nearly all light blocked */
if(tp.x < tp_eps && tp.y < tp_eps && tp.z < tp_eps)
break;
sum += (-sigma_t * (new_t - t));
if((i & 0x07) == 0) { /* ToDo: Other interval? */
tp = *throughput * make_float3(expf(sum.x), expf(sum.y), expf(sum.z));
/* stop if nearly all light is blocked */
if(tp.x < tp_eps && tp.y < tp_eps && tp.z < tp_eps)
break;
}
}
/* stop if at the end of the volume */
t = new_t;
if(t == ray->t)
if(t == ray->t) {
/* Update throughput in case we haven't done it above */
tp = *throughput * make_float3(expf(sum.x), expf(sum.y), expf(sum.z));
break;
}
}
*throughput = tp;